1. Field of the Invention
The invention relates to an arrangement for cleaning an optical window in a process, comprising means for conducting a cleaning medium to an optical window that is to be arranged in connection with a flow or the like provided in the process, the means comprising a nozzle arranged to direct a medium jet onto the surface of the optical window.
2. Description of the Related Art
Optical windows in a process are utilised today in many different industrial fields, such as food industry, paper industry, chemical industry and different research projects. An optical window may be a part in different measuring devices, such as process refractometers, which are used to determine the concentration of a solution. In a process refractometer an optical window may be provided e.g. by a prism. An example for such process refractometers is Process Refractometer PR-01 manufactured by K-Patents Oy.
The problem with optical windows arranged in a process is that they become dirty, whereby the measuring result is inaccurate and even incorrect. An example for solutions previously used in the field is a nozzle which is arranged to direct e.g. a vapour or water jet onto the surface of the optical window. Another example is the use of mechanical cleaning means, such as wipers. However, the above solutions are not sufficiently effective in difficult conditions. A drawback with nozzle solutions is e.g. their poor directability and their sensitivity to the effects of the flow to be measured. A drawback with mechanical cleaning means is their sensitivity to impurities, wherefore they operate unreliably.
On account of the above new kinds of solution have been developed in the field for reliably cleaning of an optical window even in difficult conditions. An example for such devices is an apparatus arranged in the side of the wall of a process tube that is opposite to the measuring end, whereby the cleaning means are situated at the corresponding place as the optical window at the measuring end but on the opposite wall of the process tube. The cleaning means are transferred across the process tube by means of pressurised air to be in contact with the optical window at the measuring end such that the cup-shaped member of the cleaning means surrounds the optical window. In the following step hydrochloric acid is fed into the cup-shaped member for a predetermined time. The hydrochloric acid is intended to clean the optical window. When the cleaning step has been completed, the cup-shaped member is transferred back to the initial position. The above apparatus is intended to operate particularly in measurings carried out in connection with green liquor.
A drawback with the above solution is above all its complexity as well as moving mechanisms that are easily jammed when the mechanisms become dirty. Also, the use of an acid certainly does not facilitate the use of the apparatus since the use of an acid is problematic with regard to the environment and safety at work. A further drawback is the price, which is rather high due to the complexity of the apparatus. Also the operating costs of said known apparatus are high primarily due to the great need for service.